import 'dart:math';
void main(List<String> args) {
  var random = Random();
  List ops = ['open','closed','cancel','start','end'];
  var index = random.nextInt(5);
  var command = ops[index];
  print('$index:$command');
  switch (command) {
    case 'closed':
      print('关闭系统');
      break;
    case 'cancel':
      print('取消操作');
      break;
    case 'open':
      print('打开系统');
      break;
    default:
      print("输入有误");
  }
}